In recent years, fine pattern forming methods have been actively researched and developed particularly in the field of the semiconductor industry.
Conventionally, patterns have been formed by exposure methods with high productivities, and miniaturization has been achieved by making the wavelengths of light sources shorter. However, the exposure methods have problems that mask widths cannot be reduced, controllability on mask size is poor, and there are fluctuations in mask width. Therefore, pattern formation by sidewall transfers that do not cause such problems has attracted attention. By the sidewall transfer method, a formative layer for forming a concave-convex pattern is formed on the periphery of a guide pattern formed by an exposure method or the like, and trimming is performed on the formative layer by etching, selectively leaving the formative layer. In this manner, a concave-convex pattern is formed. One of the advantages of the sidewall transfer method is that smaller patterns than the miniaturization limit that is set by the exposure methods can be formed.
By the sidewall transfer method, however, a rectangular concave-convex pattern having corners each forming almost a right angle is preferably formed in the trimming of the formative layer, and it is necessary to prevent rounding of the corners. In the formation of a rectangular concave-convex pattern, a high etching anisotropy is required, and dry etching is mainly used.
Dry etching involves both chemical etching components using chemical reactions and physical etching components using energy of particle collisions. Etching progresses isotropically in chemical etching components, and anisotropically in physical etching components. Where etching progresses isotropically, a high anisotropy cannot be achieved. Therefore, to achieve a high anisotropy, it is critical to restrain chemical etching components.
In a sidewall transfer, the formative layer for forming a concave-convex pattern is made of a single material, and accordingly, the groove side faces the groove bottom faces of the formative layer are made of the same material. Therefore, almost the same chemical etching progresses in the groove side faces and the groove bottom faces, and the etching anisotropy becomes lower. At shallow portions of the grooves, etched faces having components perpendicular to the etching direction are formed by isotropic etching. The influence of physical etching then becomes larger in those faces, and etching perpendicular to the etching direction progresses, resulting in rounding of the “shoulders.” Therefore, the sidewall transfer method has the problem that almost the same chemical etching progresses in the groove side faces and the groove bottom faces of the formative layer, and rounding of the “shoulders” occurs. Rounding of the “shoulders” means that the corners of the upper portions of the formative layer are partially removed and rounded at the time of removal of the groove bottom faces of the formative layer. In general, high rectangular properties are preferred in the shapes of etching masks in semiconductor device manufactures, the shapes of imprint patterns, and the shapes of etching masks in MTJ processing. When rounding of the “shoulders” occurs, however, a concave-convex pattern having rectangular properties cannot be formed.
Since the formative layer is formed on the periphery of a guide pattern having different film stresses, an internal stress occurs at the interface between the formative layer and the guide pattern. Due to the occurrence of an internal stress, the formative layer is warped after the guide pattern is removed. Where the formative layer is warped, the shape of the formative layer or the shape of a pattern transferred from the formative layer changes. Therefore, the problem with the sidewall transfer method lies in that the formative layer is warped due to the stress occurring at the interface between the guide pattern and the formative layer.
As described above, the conventional sidewall transfer method has the problem of rounding of the “shoulders” of the convex portions of a concave-convex pattern.